Woolie Bully socks... thin, but extremely warm. I have many thicknesses of wool socks.
Booties, either neoprene or Gore Tex. Sometimes I wear toe covers and booties.
Finally, chemical toe warmers, like you wear for winter sports. These do the trick. I use them if it's below 42 or so. Once your feet and hands are warm, the other parts are easy.
And yes, loosen your shoes. Really important.
I finally found a pair of winter road cycling shoes for women in my size (37). Am eagerly awaiting their arrival, and hoping I don't have to use all of the above things in the future. I have winter shoes for my Frog pedal bike, which are OK, but I still have to use the chemical warmers if I ride in the 30s. I am still riding outside, too, but it is supposed to get more winter like here, by the end of the week. I have a longer ride planned with DH for next Friday afternoon, so I may be put to the test.